Fertilizing Microgreens: Everything you Need to Know

Microgreens don’t need fertilizer or compost additives, but they do grow faster, deeper colored, and larger cotyledons & leaves when fertilized. Smaller seeds have less internal energy and nutrients than large seeds, and rely more on nutrients in their growing mediums (water or hydroponic).

Growing without fertilizer works for soil and hydroponic microgreens because they grow so quickly, typically 7-21 days. They are able to use nutrients already in the seed, and in the case of soil, the initial rush of nutrients liberated from wetting the soil for the first few times.

Hydroponic and soilless mixes will benefit the most from fertilizer. If you want a quick answer:

Liquid Kelp Organic Fertilizer is my favorite microgreens fertilizer.

Buy on Amazon

It’s popular, plant-based, widely available, has overwhelmingly positive reviews, and is versatile so you can use it in house plants, in the garden, for herbs and vegetables, and of course, for microgreens.

Do Microgreens Need fertilizer?

The purpose of fertilizing microgreens is to get some kind of benefit. Faster growth, deeper color, fuller flavor, or maybe even more nutrients.

But is there good evidence that microgreens need fertilizer?

No, microgreens don’t need fertilizer if grown in soil, and harvested while still young in the microgreen growth stage. Hydroponic microgreens, the ones grown on hemp mats, or in coco-coir with no nutrients, can benefit from fertilizer. That said, they will do just fine without it.

Expect faster growth, larger leaves, and deeper colors from fertilized microgreens. It’s an easy experiment to figure out which varieties make sense for you to fertilize. In general, the larger a seed or legume is, the more energy and nutrients it has already.

A smaller seed will need to absorb more from the soil, air, and water as it grows. So in my mind, it makes sense that the smaller seeds are more likely to need a higher nutrient soil or more fertilizer in a hydroponic setting when they’re first starting out.

The microgreens that need fertilizer the most are the ones that grow the longest. And technically, these will be shoots, not microgreens!

Pea shoots and anything else grown past the cotyledon stage will be the most worthy microgreens of fertilizer. But even these can get by without it.

What Soils do Microgreens grow Best In?

Microgreens can tolerate a huge range of soils. The essential thing is that the soil is moist, and it’s reasonably neutral in pH, and has the usual good soil properties:

Almost any soil will work for microgreens, but the best soil has a fine texture, good water retention & aeration, is organic, and has been tested for pathogens and stored mainly indoors to prevent insects, pests and birds from contaminating it. A more sterile soil means less mold for indoor growing.

If you want to read more about choosing soil for microgreens, and avoid a few issues I ran into, check out:

11 Tips for Choosing the Best Soil for Microgreens (Links to Article)

And if you want a wider perspective on what you can use as a growing medium for the roots to anchor to (including soil), check out this next article, there are a few surprising options.

Top Microgreen Growing Mediums: Everything you Need to Know (Links to Article)

I asked a bunch of top-tier seed suppliers what soil they recommended using for microgreens, and these were their replies:

“Really any organic soil mix would work. I would recommend testing a few varieties to see what works best for you.”

“What I suggest is the Black Gold Organic Mix. This comes in two sizes 1 cubic foot or 2 cubic foot.” It’s a well-balanced potting mix suitable for vegetables and herbs, the main ingredients are sphagnum peat moss, composted bark, earthworm castings, perlite, dolomite lime, and an organic wetting agent.

You can find the product they’re talking about on here on Amazon:

Sun Gro Black Gold Natural and Organic Soil, 2 Cubic Feet

“I don’t use soil.  I use jute mats. For larger seeds like peas or sunflowers soil is recommended and you can use a less expensive potting mix.  Anything that will retain the moisture until the seed germinates. Nutrients are not necessary as micro greens generally are harvested within 10 to 20 days.”

Should I add Fertilizer or Compost?

If you’re growing in soil, you have the option of using a richer soil (with more compost), or adding fertilizer.

So which is best?

Well, like a lot of things in gardening, it depends!

Adding compost is the most natural way to get more nutrients to your plants and seedlings, but it also comes with a bit of extra work, and a lot of extra mess.

Whereas adding fertilizer is clean, but it’s easy to add too much, and there are so many types of fertilizer out there, so how do you choose?

Overall, I’d recommend adding fertilizer over adding compost. Microgreens grow so quickly that the long-term benefits of a more compost-rich soil won’t have time to kick in.

Adding compost to soil

If you’re growing your microgreens indoors, using bagged soil, it’s pretty easy to transfer soil to your trays without making too much of a mess. But once you start to have multiple ingredients, and mixing your own soil, the chance of making a mess increase.

A lot of compost varieties also have a bit of a smell. Smelly compost indoors can be a problem for a lot of people, but properly composted materials should have an earthy, pleasant smell for the most part.

Types of compost

• Composted cow manure(0.5 – 0.5 – 0.5)
• Sheep manure (0.5 – 0.5 – 0.5)
• Mushroom Compost (1 – 0.5 – 1)
• Worm Castings (1 – 0 – 0)
• Chicken manure compost (1 – 1.5 – 0.5)

If compost you buy does have an unpleasant smell it’s likely one of two causes. It could be incompletely composted. Composting should break the manure down into a finer dark texture, and kill the majority of pathogens and pests.

The compost could also develop a smell after-the-fact if it has too much moisture, and anaerobic growth of bacteria and other organisms takes over in the bags.

Either way, if you buy compost and it has a smell, don’t risk using it in microgreens.

Are there Organic Microgreen Fertilizers?

Using organic products can not only be a health benefit, it can also help you financially if you’re selling your greens. To someone who only eats organic produce, the perceived value of your greens is zero if you’re not using organic fertilizer. That’s a huge problem!

But luckily there are a lot of great organic fertilizers on the market for you to choose from.

Organic Microgreen fertilizers come from a lot of different sources:

• Liquid Seaweed has an enormous selection online. If I had to recommend one Organic Microgreen Fertilizer (especially for hydroponics), this is it. Made from aquatic plants that grow under the sea, it’s a really nutrient dense and diverse plant food. Liquid seaweed can be made from different ingredients, but most commonly it’s made from a fine seaweed called Ascophyllum Nodosum. This is my number 1 recommendation for organic hydroponic microgreen growth. It’s the most popular recommendation you’ll find elsewhere online too. Liquid Kelp Organic Seaweed Extract 1 Gallon Fertilizer Concentrate (Links to Amazon) comes in a 1 Gallon container and goes a LONG ways (does a lot of microgreen trays), so the cost comes down substantially. You’ll definitely make your money back in denser and heavier microgreen yields with more nutrients.
• Mushroom compost might sound like composted mushrooms but it’s actually mushroom growing medium that’s been re-composted. Mushrooms are usually grown on hay, straw, corn cobs and manure. Growing mushrooms is a sensitive process, so some mushroom growers use the growing medium just once, then sell it in bags.
• Rock Phosphate is made from pure mined phosphate rocks containing 32% total phosphates. Phosphates are high in phosphorus, which promotes root growth and helps reduce transplant shock for more mature plants. It has the NPK values of 0-3-0 and comes in a 7.25 bag from Amazon and is available here (Click link to check the price).
• Feather Meal is made from hydrolyzed feathers from chickens, so it’s not a vegan option for the strict vegan. Organic Feather-based Fertilizer is probably not a great option for microgreens.
• Bat Guano is made from composted bat manure with surprisingly low odor. It has really high nitrogen with NPK 10-2-1. It’s a faster-acting fertilizer, with more nutrients available sooner (so less slow-release). Fertilizers that have more availability sooner are better for microgreens.
• Mushroom fertilizer improves soil structure and has good slow-release properties, but it’s not the best additive for microgreens. You can find it online here: Organic Mushroom Compost 5 Pound Bag
• Worm Castings can be thought of as earthworm manure. Earthworms are cultivated on a bed of peat or other suitable medium, and they consume organic matter. The manure is collected and often composted. It creates an incredibly rich, deep black compost with great well-rounded properties. This can be added to soil but not hydroponic microgreen grows. Check out online here.
• Cottonseed meal is less popular than a lot of other organic amendments. It’s a good source of primary and secondary plant nutrients including calcium, zinc, iron and other micronutrients. It’s 6-2-1 for NPK, and supplies a good ratio for robus leaf growth and deep green foliage. I haven’t experimented with it on microgreens, it s recommended for citrus trees. And despite the name, it’s actually a mix of many other meals (including fish, feather, bone, alfalfa and others). Check it out here.
• Bone Meal is particularly high in calcium and phosphorus. It can be a great amendment for soils, but isn’t particularly recommended for hydroponic microgreens. Find pricing and buy online here.
• Fish Emulsion isn’t ideal for microgreens. While it provides a lot of nutrients, it’s risky business indoors because of the smell. You probably want to stay away from fish emulsion for microgreens.
• Blood meal for microgreens is one of the highest nitrogen sources of all the organic fertilizers. It’s sterilized, dehydrated blood from slaughter houses. Microgreen growers may prefer to stay away from blood meal because of its source. It Is fully organic, and a great additive for outdoor gardens or soil grows if you’re comfortable using animal-product derived soil amendments.
• Crushed Montmorillonite for microgreens is available made in the USA marketed as a product called Azomite. It’s actually marketed specifically for microgreens by one of the largest microgreen seed suppliers: True Leaf Market. It’s made from crushed minerals, containing over 60 different nutrients and micronutrients. The next section has a link to Azomite from True Leaf Markets, or you can check it out on Amazon here.
• Alfalfa Meal for microgreens can work, but I wouldn’t recommend it. Alfalfa meal is usually recommended for blooming plants to support faster flowering and longer duration. It’s generally 3-0-3, and while it does have good nutrients, it also has starches and sugars. Starches and sugars in microgreen soils, especially indoors, is a recipe for microorganism growth. Mold, bacteria and insects will be drawn to it, so unless you’re looking for new room-mates, I would avoid Alfalfa meal for microgreens.

What Fertilizer does True Leaf Market Recommend?

True Leaf Market recommends using Azomite. Source.

It’s OMRI Listed (certification pma-9115) certified organic. They recommend using ½ Teaspoon per 10” x 20” tray. The product is a powdered trace mineral. It’s made from naturally occurring montmorillonite (a mineral) from Utah. Containing over 60 trace minerals and essential nutrients, microgreens are able to absorb some of these, and pass them on to you in bioavailable form.

It may add a little bit of expense to your grow, but not much. At $10 for a 2lb bag it will go a long ways.

What’s the best liquid microgreen Fertilizer?

There are a lot of options for liquid microgreen fertilizers, but if I had to choose one I would recommend an organic liquid kelp. There are a few reasons for this:

• It’s so popular. The crowds have spoken on this one. Liquid kelp is available almost everywhere, there is great selection, and if you look at the reviews: people are overwhelmingly happy. Leverage the years other microgreen growers have put into testing.
• Liquid kelp won’t introduce any strange flavors to your microgreens (like fish emulsions and some other fertilizers).
• It’s plant-based, unlike bone meal, blood meal, and some other meals which are blends containing animal products. Animal products introduce some potential problems.
• Marketing: Animal-product-free fertilizers can be a good marketing point for microgreens. Some microgreen customers will be vegetarian or vegan, and a lot of them would be happy to hear that your fertilizers are 100% plant based. Think about putting this on your website, or mentioning it to friends and family if you’re selling microgreens on the side.

You can pick up a great liquid kelp fertilizer from Amazon at the following link, it will last you quite a while, and you can use it in house plants or in the garden too, so it’s money well-spent.

Liquid Kelp Organic Seaweed Extract 1 Gallon Fertilizer Concentrate (Links to Amazon)

What’s the best overall microgreen fertilizer?

The best overall microgreen fertilizer is going to depend on what you’re growing in, and I would lump this into two main categories:

• Growing mediums with nutrients built-in
• Hydroponic and Soilless mixes (low nutrients)

Nutrient-free growing mediums

A nutrient-free growing medium is going to include most hydroponic growing mediums: hemp pats, coco-fiber pads, coconut coir, rockwool, burlap, and nutrient-film technique and ebb and flow hydroponic systems. Its also going to include soilless mixes. Mixes that look like soil, but lack any major source of nutrients.

For low nutrient growing mediums I definitely recommend adding a fertilizer. It will give darker greens, thicker growth, and more yield, offsetting the cost of the fertilizer.

Overall, the best microgreen fertilizer in this situation is a liquid kelp. I’ve recommended it before in this article, and that’s because it works. I could recommend 10 different fertilizers, but if it works it works.

Liquid Kelp Organic Seaweed Extract 1 Gallon Fertilizer Concentrate (Links to Amazon)

High-nutrient growing mediums

High nutrient growing mediums are going to include any potting mixes, seedling starting mixes, vegetable and herb mixes, and any other soil mixes that have compost or some form of nutrient mixed in.

For these mixes I find that it’s probably not worth the extra trouble of adding fertilizer. Just buy a good organic soil that’s a little higher in nutrients, and you can cut out the added step of fertilizing.

For a great organic soil that’s high in nutrients you can get away with using a lot of different options, but one that’s worked well for me is this one:

Epsoma 8 Quart Organic Potting Mix (Links to Amazon)

It’s has a fine texture (easy to spread for microgreens), and retains moisture well to prevent drying out.

Do hydroponic microgreens need fertilizer?

Microgreens grown hydroponically will see the biggest benefit from fertilizer.

Growing media with no inherent nutrient value (like fiber mats, hemp, jute, or rockwool), and especially when combined with slower growing varieties are at the top of the list for needing fertilizer.

But, you can get away without fertilizer when growing hydroponically, especially for faster growing microgreens, and microgreens with larger seeds (more energy and nutrients built-in) like pea shoots and sunflower microgreens.

Adding fertilizer can significantly increase hydroponic yields, and is definitely worth investigating. Use high quality hydroponic additives, and organic where you can, and your microgreens will blow you away.

A properly managed hydroponic grow yields the highest microgreen productivity of any growing style, but it’s more labor intensive and takes more startup capital and training.

What’s the best Hydroponic Microgreens Fertilizer?

FloraGro is a water-soluble fertilizer by General Hydroponics that’s designed to be well-balanced and boost structural and foliar growth. It has NPK of 2-1-6, meaning 2% Nitrogren, 1 % Phosphorus, and 6% Potassium.

FloraGro is pH balanced, so it won’t alter the pH of the water you’re adding it to. True Leaf Market (a source I trust for microgreen information, and a prolific seller of microgreens seeds) recommends using 3 teaspoons of FloraGro in each gallon of water used once the cotyledons have emerged.

It’s supposed to give larger leaves than would otherwise grow.

I think it would be worth experimenting with using FloraGro for a few days right in the middle of the microgreens grow, but stopping it a few days before harvest and watering with pure water. I suspect that the hydroponics fertilizer will modify the flavor of the final microgreens, but I haven’t tested this myself.

What are nutrient solutions?

A nutrient solution is the final liquid that makes contact with the roots of your microgreens in a hydroponic setting. It’s the carefully crafted mixture of water, fertilizers, trace minerals and anything else you’ve decided is worth the trouble.

The simplest nutrient solutions use on-site water with added fertilizer. The next step up in complexity is pH balancing.

Achieving the correct pH in a nutrient solution is critical for proper nutrient uptake. The roots of your microgreens can only absorb certain nutrients at certain pH ranges, so if your pH is too high or too low, you microgreens may yellow or have poor flavor and nutrition.

The ideal pH range for most hydroponic crops is between 5.5 and 6.5 but it varies depending on species.

Conclusion

Thanks so much for reading this far (or did you just skip down to the end?)!

Choosing a fertilizer for microgreens can be a real pandora’s box. Once you start looking around the options are almost endless.

Overall I’d recommend a Liquid kelp (sea-weed based) fertilizer if you’re adding nutrients to a hydroponic grow mat, or soilless mix grow.

If you’re using soil, just use a higher nutrient soil, like a good organic potting mix instead of adding fertilizer. It will save you trouble and give you great results.

If you’re selling microgreens, or are a vegan or vegetarian yourself, consider the impact of animal based products. Blood meal, bone meal, fish emulsion, and other animal-based ingredients could be a strike against you if your customers found out. It really depends on your situation, but it’s worth keeping in mind.

Next Steps

If you’re considering fertilizers because you’re having trouble getting the yields you want, it could be because you’re missing an important step in the growing process. Check out my article that quickly walks through the key steps here:

How to Grow Microgreens in 11 Easy Steps (Updated 2020) (Links to article)

And if you’re getting into selling microgreens, I’ve started writing a series to help you get your business off the ground:

Packaging for Microgreens – Giant Sourcing Guide with Tons of Options (Links to article)

Creating Label Stickers: How to Sell Microgreens (Links to article)

Sources

• Questions regarding pH dynamics and adjustments.
• What is a nutrient solution? Science Direct
• True Leaf Market: Fertilizing Microgreens
• FloraGro by General Hydroponics
• Yield and quality of basil, Swiss chard, and rocket microgreens grown in a hydroponic system (R Bulgari et al 2017)
• Nutrient content of cabbage and lettuce microgreens grown on vermicompost and hydroponic grow pads (CF Webber 2016)
• Light intensity and quality from sole-source light-emitting diodes impact growth, morphology, and nutrient content of Brassica microgreens (JR Gerovak et al 2016)
• Microgreens for Human Nutrition in Spaceflight (CM Johnson 2019)
• https://ntrs.nasa.gov/search.jsp?R=20190033178